A typical industrial clarification installation comprises a plurality of reservoirs or holding tanks to be filled with mill effluent. Clarification is normally effected by alternatively agitating and letting the effluent settle, and lifting floating scum from the surface of the effluent or scooping sediments at the bottom of the reservoir. These holding tanks are generally equipped with mechanical equipment that must be accessible for inspection, maintenance or for repair.
The clarification process is often accompanied by a fermenting action and a generation of odorous bio-gases, and/or the release of volatile organic carbons. For environmental reasons, these gases must be collected and treated. Therefore, a clarification reservoir, or clarifier, is preferably covered and sealed to contain the gases. Also, a clarifier preferably has a piping system to transport the gases to a gas treatment plant.
When a removable flexible cover is installed over a clarifier, the installation must resist wind forces that tend to flap portions of the cover and stretch it laterally. Also, the attachment of a flexible cover must be sufficiently strong to permit one or more workers to walk on the flexible cover to fix it if the need arises.
A clarifier having a removable flexible cover mountable thereon must also provide for a certain level of safety when the cover is removed. During maintenance activities for example, it is common to find power tools, welding machines, acetylene torch carts and maintenance wagons along the perimeter of the clarifier. It is therefore important to prevent workers and equipment from sliding into the reservoir.
Examples of various systems available for covering a reservoir are described in the following documents:                U.S. Pat. No. 3,195,310 issued on Jul. 20, 1965 to C. E. Schroeder;        U.S. Pat. No. 4,324,370 issued on Apr. 13, 1982 to W. Guard et al.;        German Patent DE 2,938,496 published on Apr. 24, 1980;        French Patent FR 2,668,195 published in Apr. 24, 1992.        
Although the flexible covers of the prior art deserve undeniable merits, it is believed that these systems do not meet all the requirements for a flexible clarifier cover which is securely mountable, removable and safe. It is believed that there continues to be a need for a new removable flexible cover which may be positively sealed, which can support workers walking thereon and which provides for a safe working environment.